Part of the challenge of running a table top role-playing game is coming up with ideas that make the campaign memorable. One way that seems to work for my group is through quirky rewards. I can't remember when I first saw the item I'm going to be talking about today, but it left an impression on me and I hope that others can find it. I am also going to go over a few different variations of a soul bounded sword. It will be aimed at 5th edition D&D but should be easy to convert to other systems. The general ideas are easy to apply to other weapons as well. As always, feel free to change the DCs.
The basic idea behind this weapon is a very simple one and can be seen throughout D&D history with monsters like the lich and the death knight. Through magic, a character's soul is connected to the weapon and as a result there are certain bonuses they receive. This kind of weapon is typically given to non-player characters but with care can also be given players as well.
The Soul Bounded Sword
“The weapon, seemingly of good quality and make, chips easily with every swing you make. To make matters worse, you feel pain flare with ever chip as scratches appear on your body.”
Every time a character attacks with this sword and deals damage, the bound character loses the same amount of hit points (if they attack a creature with 2 hit points left and roll 6 damage, the bound character takes 2 necrotic damage). Casting remove curse on the sword frees the character and also removes the curse on the item, making it a non-cursed magic item. Casting remove curse just on the bound character severs the link with the weapon but the item remains cursed. Destroying the weapon kills the character bound to it. If the character bound to the sword is killed, the next character to touch the sword is bound (there are ways around this, such as tongs or magic gloves). While not bound to a soul, it has no bonuses.
Note: As written above, if a player wrestles away the soul bounded sword from a character and proceeds to attack the bound character with their soul bounded sword, they will do double damage. They can also wrestle it away and destroy it, thereby killing the character bound to the sword.
Addition 1: You can allow the bound character to sense where the item is and if it has been moved. This way, they at least have some benefit from the curse.
Addition 2: You can allow the bound character to call the weapon to themselves by using their bonus action or their one interaction with the environment as part of an action as decided by the character.
Addition 3: Through the connection, the sword can subtly influence the character's actions. Roll a Wisdom saving throw when the bound character is attempting to draw a weapon (DC 15) and the soul bounded soul is within reach. Upon failure the character, unconsciously and without noticing, grabs the cursed weapon. (The saving throw can be changed to charisma to be more like resisting the charm spell or the player can choose between the two).
Addition 4: Wearing gloves while touching the sword does not cause it to be bound to you.
Addition 4: The curse is quite powerful. Roll an Intelligence (Arcana) check (DC 20) when an identify spell is cast on the weapon. On a success, the curse is identified.
Alternate 1: If more incentive to use the cursed weapon is desired, change the damage that the bound character receives from the sword to 1/2 that they dealt.
Alternate 2: In the hands of the character that is bound to the sword, it functions like a normal sword. However, it becomes weakened when separated from its owner and at that point begins to chip.
Alternate 3: Roll a Wisdom saving throw (DC 15) when a character first touches a bounded soul sword that is currently bound to no soul. On a success, they start to feel something is wrong and can choose to drop the sword. Afterwards, the sword tries to bind itself to the character holding it. The character cannot mistake the sword's attempts to bind them now (describing the swords attempts and attack should be left to the Dungeon Master and vary case by case). Roll a Charisma saving throw (this is meant to be like a charm spell) (DC 15) on a success, they resisted it long enough to try to drop it. If they do not drop it, they have to make the saving throw again at the start of every round or after every 5 seconds.
The above options can all be combined and used together in order to create many different kinds of items based on the same concept. An addition is something brand new where an alternate will change something originally written.
In the World
To provide incentive for players to buy these weapons, the sword can be made 1/2 the price of a sword with the same bonus. It should also cost 1/2 the cost to make compared to the item with the same bonus, if you can bound the characters soul during the construction process (this is easy to do if they are willingly part of the process because they think they are getting a magic weapon or when they actually want the item as is). In the magic black market, such cursed items could be regularly pushed on unsuspecting customers at full price. If this is part of your desired world, addition 4 should probably be used.
Whether the weapon should cost the same to make compared to the item with the same stats should be decided on a game by game basis (this is when the original bound soul is not part of the process). In general, if it costs
Also of note, this kind of weapon can actually be desirable with alternate 1, alternate 2, addition 1, addition 2 and if offered for half price. They do come with the drawback when separated from their owner.
This kind of sword can be used as the first step of creating a lich or death knight, if so desired. The next step could be a series of rituals that prevent the character from aging when bound to the sword and the last could be the rituals that allow a character to gain their undead powers.